One of the families traditionally placed within the Rhodophyta is the Solenoporaceae. Although several genera were initially assigned to the animal kingdom (e.g., as tabulate corals, bryozoans, or sponges; see Cozar and Vachard, 2006), solenoporaceans were later generally interpreted as calcified red algae (Pia, 1927) (FIG. 4.45). Today, however, the Solenoporaceae is known to represent a heterogeneous group that includes a variety of animals, red algae, and cyanobacteria, and, as a result, it is no longer possible to support the concept of the Solenoporaceae (Ordovician-Miocene) as a coherent family (Riding, 2001).

Solenoporaceans were nodular or encrusting marine organisms composed of closely packed, radially or vertically divergent rows of tubes. Their diameters were almost always larger than those of living coralline red algae (see section "Other Calcified Red Algae"), which are believed to be related structurally. One common representative is Solenopora (FIGS. 4.46-4.48), established for irregularly lobed, calcium carbonate masses composed of radiating, juxtaposed tubes with shared walls. The type species, S. spongioides from the Upper Ordovician of Estonia, was initially interpreted as a chaetetid sponge, but later transferred to the red algae. Reexamination of the original illustrations and new material from the type locality, however,

FIGURE 4.45 Julius Pia.

indicates that the initial interpretation was accurate and thus removes Solenopora from the algae (Riding, 2004). Another form initially placed in Solenopora is S. gotlandica from the Silurian of Sweden and Wales. This species, which represents a true red alga, was transferred to the genus Graticula (Brooke and Riding, 1998, 2000). Skeletons of G. gotlandica (FIGS. 4.49, 4.50) may be free nodular or massive encrusting and are composed of laterally joined columns, branches, or pillars, which are mushroom- or umbrella-like, and occasionally up to 10 cm high (Nose et al., 2006). The columns consist of erect-to-radiating, juxtaposed filaments, which are rounded to polygonal or irregular in cross section, and which share adjacent walls; cross partitions (cross walls) in adjacent filaments are sometimes aligned. The arrangement of cross partitions, along with the presence of sporangia in sporangial compartments arranged in irregular sori, separates Graticula from other forms traditionally placed in the Solenoporaceae. Based on these features, Brooke and Riding (1998, 2000) established the new family Graticulaceae, which they assign to the Corallinales. The Paleozoic Graticulaceae are structurally similar to the Sporolithaceae (Corallinales); the type species G. gotlandica closely resembles members in the earliest recorded modern Corallinales, whose fossil record only extends back into the Early Cretaceous (Braga and Bassi, 2007; Tomás et al., 2007).

The solenoporacean genus Parachaetetes is found as early as the Late Carboniferous, and Cenozoic forms are especially common in shallow-water reef facies (Wray, 1977). It occurs as bluntly lobed growths up to several centimeters in diameter. In vertical thin sections, typical forms exhibit a tightly packed mass of elongate cells arranged in curved radial lines. In cross section, these cells are circular and variable in length. At least some species within the genus Parachaetetes

Encrusting Corallinales
FIGURE 4.46 Solenopora sp. (Jurassic). Bar = 2cm. (Courtesy M. Nose.)
Solenopora Jurassica

FIGURE 4.49 Red algal-calcimicrobe boundstone with Graticula gotlandica (Silurian). Bar = 5 cm (Courtesy M. Nose.)

FIGURE 4.47 Solenopora condensata (Jurassic). Bar = 2cm (Courtesy M. Nose.)

FIGURE 4.49 Red algal-calcimicrobe boundstone with Graticula gotlandica (Silurian). Bar = 5 cm (Courtesy M. Nose.)

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